Speaking of Hubble...

Archive: October 2012

The Lure of the Exoplanet Next Door

October 31, 2012 by Ray Villard
Artist’s impression of the the planet orbiting the star Alpha Centauri B. CREDIT: ESO/L. Calçada/N. Risinger

Artist’s impression of the the planet orbiting the star Alpha Centauri B. CREDIT: ESO/L. Calçada/N. Risinger

Despite the hundreds of extrasolar planets found so far, the discovery of a planet orbiting the nearest star to our Sun has extraordinary consequences for astronomers and the public alike.

The Sun’s nearest neighbor is a multiple star system that lies merely 4.3 light years away – a galactic stone’s throw.

Alpha Centauri is only clearly visible from southern skies as a brilliant white star (it is actually two stars that are too close together to be seen separately by the naked eye). The faint third member of the system, a red dwarf star Proxima Centauri, yields no evidence for planets and is so far from the binary pair as to be inconsequential.

The European Southern Observatory reported the planet discovery on October 17. An instrument called the High Accuracy Radial velocity Planet Searcher, or HARPS, precisely measured small wobbles in the slightly smaller companion star, Alpha Centauri B. This yielded telltale evidence for the presence of an Earth-sized world whirling around the star, completing an orbit every 3.2 days.

The bad news is that the planet is too close to the star to support life as we know it. The surface roasts at over 2,000 degrees Fahrenheit – hot enough for hellish oceans of molten magma.

Alpha Centauri A & B are separated by as much as two billion miles. According to models, they are each capable of forming terrestrial planets despite the perturbing influence of a binary companion. In fact, a companion star can be a gravitationally stabilizing influence, like massive Jupiter is in our solar system.

On the heels of this discovery, the Alpha Centauri system is ripe for far-future exploration. That’s because NASA’s planet-hunting Kepler observatory is showing us that entire planetary systems are common. Kepler has identified several thousand other exoplanets, though most remain to be confirmed by follow-up observations.

What’s more, Kepler is finding that rocky Earth-sized planets are increasingly common. (Kepler is monitoring over 150,000 stars in the constellation Cygnus for telltale planet transits, and Alpha Centauri is not in its field of view). Therefore, it’s probably only a matter of time before other observations turn up additional planets at Alpha Centauri.

It’s also possible that one or more planets could be in the stars’ habitable zones, where temperature are mild enough for stable oceans to exist. The discovery of such a world would eventually be followed by a large enough optical-infrared space observatory that could spectroscopically sample the planet’s atmosphere. Attempts would also be made with NASA’s upcoming 6.5 meter mirror James Webb Space Telescope.

If spectroscopic observations made perhaps with an 8- to 16-meter mirror space telescope confirmed that a planet’s atmosphere has biotracers – such as oxygen, ozone, nitrous oxide, methane, and chlorine – there would be motivation to build a dedicated interferometric array of optical space telescopes. Observations could reveal the waxing and waning of continents and oceans as the planet rotates, and the changing tapestry of weather patterns. SETI observations would monitor the planet for evidence of alien telecommunications.

Today’s fastest space probes would take 40,000 years to get to Alpha Centauri. But by the next century, there could be attempts to send a small probe to the system at extraordinarily faster speeds. Such a mission would have a cruise phase of only 40 years if the technology were to develop for extraordinarily powerful propulsion systems that could accelerate a probe for 10 percent the speed of light. That no small task, but it doesn’t require some imaginary warp drive, simply Newtonian physics. The builders of the spacecraft could live long enough to see data returned from Alpha Centauri.

An ambitious mission would enter orbit around any potentially habitable planet. Robotic landers would be dispatched to observe life up-close and personal. We could behold the effects of Darwinian evolution on an extraterrestrial Serengeti of unimaginably exotic creatures.  By the time we are ready for such a mission we will have matured the required artificial intelligence and nanomachine technology. The autonomous probe would direct its own exploration mission.

Because Alpha Centauri A and B are Sun-like in terms of age and temperature, there has been plenty of time for life to develop on any planets we might find in the habitable zones around either star.

The view from a terrestrial planet in an approximately Earth-sized orbit around Alpha Centauri would certainly be exotic to our experience.  At one point during the planet’s year, the two stars would be in conjunction – in other words, side-by-side in the sky. The closer star would have a glowing disk like the Sun; the other would be more star-like and far more brilliant than Venus.

A planet would be influenced by the radiation from both stars. Every 70 years Alpha Centauri A & B come closest to each other. Warming on an Earth-like world would be brief but intense, raising planet-wide temperature by a few degrees.

Given the awesome power of biological evolution, life would evolve to cope with living with a second star. Life on such a planet might develop two circadian rhythms corresponding to both the length of day on the planet, and orbital period of the binary stars.  There may be planet-wide migrations in anticipation of the approaching “super-summer.” And, there would be a variety of other novel coping mechanisms.

If there were intelligent life present out there, Alpha Centauri astronomers would routinely turn their attention on a bright first-magnitude star in the W-shaped constellation Cassiopeia. It would be our Sun. And the astronomers might muse on what life would be like around a single yellow dwarf star.

Gazing Deeply into the Universe

October 8, 2012 by Frank Summers
Hubble’s eXtreme Deep Field

Hubble’s eXtreme Deep Field

On September 25, 2012, Hubble released another “deepest image ever taken of the universe,” this one called the Hubble eXtreme Deep Field. This image shows more galaxies, fainter galaxies, and farther galaxies than any other image before it. Within the new deep field image are a handful of galaxies located about 13 billion light-years away. And, since the light from those galaxies has taken 13 billion years to cross the intervening space, we see these galaxies as they were less than a billion years after the beginning of the universe.

We can look out in space, and thus back in time, to see galaxies and the formation of galaxies just after the Big Bang. How’s that for a deep thought? Consider it as you watch this video showing the tiny 2D area and vast 3D extent of the Hubble eXtreme Deep Field:

CREDIT: NASA, ESA, and G. Bacon, F. Summers, and Z. Levay (STScI)

Astronomers call such long exposures “deep” because fainter objects tend to be farther away, hence, a longer exposure sees deeper into the universe. The new deep field is the latest in a line extending back to the original Hubble Deep Field (HDF), released in 1996. That breakthrough observation was followed by the HDF South (1998), the Great Observatories Origins Deep Survey (2003), the Hubble Ultra Deep Field (HUDF, 2004), and the HUDF09 (2009).

The Hubble eXtreme Deep Field builds upon the HUFD09 image by adding all Hubble observations that, done for a variety of research programs, cover the HUDF field on the sky. In that sense, it should perhaps be called the HUDF12, but that’s less catchy and trendy than calling it “extreme.”

However, calling it extreme does have its perils as well. It implies that Hubble will never exceed it, which is wrong. Observations continue to be taken and two programs in particular will add significantly to the data set. One will continue to add to the infrared portion of the image, as was the major improvements seen in the 2009 and 2012 deep field images. Another will flesh out the ultraviolet observations in a program one colleague jokingly referred to as “deep purple.” (Younger readers should look that up on Wikipedia while older readers immediately start humming the intro guitar riffs to “Smoke on the Water.”)

Will there ever be a “deepest” image? The answer can be both “no” and “yes.”

No, there will just be a series of “deepest yet” images, as astronomers will continually build new instruments and new telescopes enabling better observations. Deep fields with the James Webb Space Telescope are already eagerly awaited.

But also “yes,” if one thinks in terms of depth in space. As we look farther out in space and further back in time, we will get to a point before the first stars and galaxies formed. Earlier than about 100-200 million years after the Big Bang, there may be no light to see. We can, in the not-too-distant future, reach the edge of the observable universe.

Whoa. Now that’s deep.